Two-way communication system with selective muting

Abstract

A bidirectional communication channel provides communication across a sound proof wall used, for example in a ticket booth. Normally communication from outside into the booth is muted by inhibiting the gain of a listen channel to a preselected percentage of its maximum gain level. After an attendant talks into an internal microphone, the muting is temporarily inhibited and normal communication is allowed between an attendant and a customer. After the conversation is completed, the system reverts back to a muted operational mode.

I claim: 
     
       1. A bidirectional communication system for providing communication between two points, said system comprising: a listen channel including a listen microphone, a listen speaker and listen amplification means for transferring signals from said listen microphone to said listen speaker at one of a first and a second gain to reproduce sounds from said listen microphone at a corresponding first and second volume, said first gain being lower than said second gain;   a talk channel including a talk microphone, a talk speaker and talk means for transferring signals from said talk microphone to said talk speaker; and   control means for controlling said listen channel, said control means including talk sensing means for sensing talk signals in said talk channel, said control means selecting said first gain under quiescent conditions, and said second gain after said talk signal has been sensed.   
     
     
       2. The system of claim 1 wherein said control means includes mode defining means for defining a talk mode initiated when said talk signals are sensed, and a listen mode succeeding said talk mode, said listen channel being set to said second gain during said listen mode. 
     
     
       3. The system of claim 1 further comprising inhibiting means for selectively inhibiting said listen channel when said talk signals are sensed. 
     
     
       4. The system of claim 1 further comprising inhibiting means for inhibiting said talk channel when said talk signals are not sensed. 
     
     
       5. A communication system for exchanging voice signals across a sound proof barrier defining an outer area and an inner area, said system comprising: a listen channel having a listen microphone in said outer area, a listen speaker in said inner area, and listen amplifier means for transmitting listen signals from said listen microphone to said listen speaker at one of a high and a low gain to reproduce voice signals from said listen microphone at one of a respective first and second volume;   a talk channel including a talk microphone disposed in said inner area, a talk speaker disposed in said outer area and talk amplifier means for transmitting talk signals from said talk microphone to said talk speaker; and   control means including means for sensing talk signals and means for setting said listen channel to said high gain in response to said talk signals, and for setting said listen channel to said low gain a period of time subsequent to said talk signals.   
     
     
       6. The system of claim 5 wherein said control means includes means for defining a talk mode when said talk signals are sensed, and means for defining a listen mode subsequent to said talk mode, wherein said listen channel is set to said high gain during said listen mode. 
     
     
       7. The system of claim 6 wherein said control means includes mens for defining a quiescent mode, wherein said listen channel is set to said low gain in said quiescent mode. 
     
     
       8. The system of claim 7 further comprising inhibiting means for inhibiting said listen channel in said talk mode, and said talk channel in said listen mode. 
     
     
       9. The system of claim 5 wherein said control means includes means for generating a timing signal extending a first predetermined period after said talk signals have terminated. 
     
     
       10. The system of claim 9 wherein said first period is about 200 msec. 
     
     
       11. The system of claim 5 further comprising means for generating a command signal after said talk signals have terminated, said command signal setting said listen channel to said high gain. 
     
     
       12. The system of claim 11 wherein said command signal has a predetermined duration. 
     
     
       13. The system of claim 12 wherein said duration is about 20-60 seconds. 
     
     
       14. The system of claim 12 wherein said duration is about 30 seconds. 
     
     
       15. The system of claim 5 further comprising control inhibit means for inhibiting said control means wherein said listen channel is set to said high gain when said inhibit means is activated. 
     
     
       16. The system of claim 15 wherein said inhibit means is a manual switch.